1. Field of the Invention
The present invention relates to an image communication apparatus equipped with an IP facsimile function that has a plurality of synchronous serial interfaces, as well as a signal processing unit, and more particularly to a transfer timing of a PCM (Pulse Code Modulation) interface that transfers PCM data.
2. Description of the Related Art
In recent years, conventional circuit-switched telephone networks are being replaced with networks based on IP (Internet Protocol) technology, and technology that provides services over a LAN or a Next Generation Network (NGN) is in widespread use. Here, the term “NGN” refers to an IP network in which the network itself is equipped with a bandwidth guarantee function and a security function to integrally realize a telephone service, a video communication service, a data communication service, and other such services.
Further, SIP (Session Initiation Protocol) that is a protocol with which a virtual session is established between communication devices on such a LAN or NGN and which guarantees services while the session is established is in widespread use. Various kinds of services have been proposed that use a protocol such as IP or VOIP (Voice Over IP) to allow a telephone call or image communication to be performed, or both a telephone call and image communication to be simultaneously performed, at a communication device at which a session was established using the SIP. Further, with respect to such image communication, facsimile communication based on a digital facsimile protocol described in ITU-T Recommendation T.38 and facsimile communication based on a digital facsimile protocol described in ITU-T Recommendation T.30 (T.30 facsimile communication by VOIP deemed voice) and the like are also available.
In such voice communication or image communication, the PCM data is transferred to respective processing units through a plurality of PCM interfaces inside an image communication apparatus. For example, Japanese Patent Laid-Open No. 2005-202643 discloses technology that uses a synchronous serial bus that includes a data signal line and a synchronous signal line, in which one party in a transfer operation is caused to operate as a master and another party is caused to operate as a slave. Further, in the case of selectively switching a plurality of slaves to connect with a master and performing PCM data transfers with respect to the plurality of slave also, similarly to the foregoing technology, one party in the transfer operation is caused to operate as a master and another party is caused to operate as a slave, and transmission and reception of bidirectional data is performed based on the transfer timing of the respective masters.
However, the following problem exists in the above described conventional technology. At a plurality of different PCM interfaces, communication between masters and slaves is performed using a different transfer timing for each master. Consequently, since a series of processing operations is performed in a distributed manner, in some cases the same data is transferred between the respective PCM interfaces. In such a case, it is necessary to transfer the same data at PCM transfer timings that are different at the respective masters of the plurality of PCM interfaces, and therefore the control is complicated and such a situation leads to a decrease in performance due to an increase in the control load.
According to the above described control, by storing transfer data in a memory of the like, read operations are performed so as to avoid conflicts arising between the transfer timings of different asynchronous masters, and the control is executed so that the same data is supplied between the respective PCM interfaces. In addition, while the same data is being transferred among the respective PCM interfaces, it is necessary to perform control to prevent writing of the next transfer data in order to protect the current transfer data or the like, and there is thus the problem that the control load increases.